The invention concerns a seal device for a submersible machine such as a pump or a mixer.
A machine of this type normally comprises an electrically driven motor and a hydraulic unit with an impeller connected to the motor via a rotary shaft.
In order to prevent the medium within the hydraulic unit from entering the motor along the shaft, one or several seals are arranged between the hydraulic unit and the motor. A common type of seal is the so-called mechanical seal which comprises a seal ring rotating with the shaft and a stationary ring attached to the surrounding housing. The two seal rings are pressed against each other by spring force preventing medium from entering between the seal faces.
If the medium within the hydraulic unit contains pollutions those may, as the pressure is higher in the hydraulic unit, enter between the seal faces and damage them causing a bad seal result.
It is thus common to arrange two mechanical seals parted by a room filled with oil which lubricates and cools the seal faces. In this way the seal adjacent the motor will always operate with a clean medium thus diminishing the risks for damages. If the seal adjacent the hydraulic unit should be damaged, medium may enter the oil housing, but by controlling the oil at certain intervals the damaged seal may be replaced before the oil has been too diluted. An example of such a solution is shown in the Swedish Patent No. 381 318.
If it has been noted that the dilution of the oil has gone beyond a certain limit, the seal adjacent the hydraulic unit must be replaced. If the dilution has gone very far, the other seal might have been damaged as well and thus it is often advisable to replace both seals at the same time.
In order to simplify replacement of the seals it has been suggested to connect the two seals into one single unit. An example of such a solution is shown in the Swedish patent No. 200 144 (U.S. Pat. No. 2,950,931). This construction shows many advantages, but because of the great number of details it is too expensive to be used extensively. In addition to that, the attachment of the seal means is carried out by the pump impeller causing axial loads which might damage the seal rings and mean bad alignment. This invention is a further development of this known device where the disadvantages have been eliminated.